The conventional fan mainly includes a plurality of blades along a rotary shaft. The plurality of blades extend from the rotary shaft. When a driving device at a rear side of the rotary shaft drives the rotary shaft to rotate, the blades are driven to rotate and thus air are driven to flow along a predetermined direction.
However, in the prior art fan structure, the blades are arranged around the rotary shaft. When the blades rotate, the wind becomes smaller and smaller along radial inward directions. Therefore the wind disperses outwards and thus, the wind cannot be concentrated. As a result, the wind strength is insufficient.